2 Measurement

Several definitions of measurement exist. One of the earlier ones is by Stevens (1946, p. 677) who, paraphrasing Campbell stated that “… measurement, in the broadest sense, is defined as the assignment of numerals to objects or events according to rules.” In fact, the definition would probably be more precise if we state that the assignment is made to certain characteristics of the objects, persons, events, etc.

2.1 Measurement scales

As stated by Stevens (1946), numerals are assigned, but many times these numeral does not express a quantitative measure, but rather some sort of a category, that some sort of quality. Stevens distinguished four different types of measurement scales based on the notion that differences in the rules of the assignment of numerals may lead to differences in the resulting measurement scales. This distinction is based on the mathematical characteristics present in the scales. The simplest scale is such that the possible values of the variable are transformed to numbers, but these numbers do not bear any characteristics of numbers, even the ordering of the values is arbitrary. Such measurement scales are called nominal scales. The next level is that of the ordinal scales where the ordering of the values is not arbitrary any more, but the distances between the subsequent values are not meaningful, nor the ratio of the values. In case of the interval scales the values can be meaningfully ordered, and the difference between the values can be interpreted, whereas in case of ratio scales also the ratio of the values can be interpreted, such a scale has an absolute zero value.